1. Field
The present invention relates generally to data communication. More specifically, the present invention relates to techniques for selectively updating base station identifiers that may be used for position determination purposes.
2. Background
It is often desirable, and sometimes necessary, to know the position of a wireless user. For example, the Federal Communications Commission (FCC) has adopted a report and order for enhanced 911 (E-911) wireless service that requires the location of a wireless terminal (e.g., a cellular phone) to be provided to a Public Safety Answering Point (PSAP) each time a 911 call is made from the terminal. In addition to the FCC mandate, service providers have begun to recognize that location services (i.e., services that identify the position of a wireless terminal) may be used in various applications to provide value-added features. For example, a service provider may use location services to implement location-sensitive billing, provide location-sensitive information (e.g., driving directions, traffic report, nearest gas stations, and so on), and provide location-related services (e.g., asset tracking, asset monitoring and recovery, fleet and resource management, and so on).
The position of a wireless terminal may be determined based on (1) distances to a sufficient number of transmitters, which are used as reference points, and (2) the locations of these transmitters. The transmitters may be satellites of the well-known Global Positioning System (GPS), base stations of a wireless communication network, or a combination of both. The terminal can estimate the distance to each transmitter by measuring the time required for a signal to travel from the transmitter to the terminal. The location of the transmitters may be provided within the signals themselves or from another entity in the network. A position estimate may then be computed for the terminal based on the estimated distances to the transmitters and their locations.
A position determination entity (PDE) within the wireless communication network may provide some of the information needed to compute a position estimate for the terminal. This “aiding information” may include the location of the base stations, timing information, and so on. Depending on the whereabouts of the terminal within the network, the PDE may provide different information. For example, depending on the specific cell in which the terminal is currently located, the PDE may provide only the locations of base stations that may be received by terminals within that cell.
A large communication network may be composed of multiple systems, each of which may include a number of base stations. “Base station identifiers” may uniquely identify each base station in the network. Base station identifiers can comprise a base station identifier (Base ID), a system identifier (SID), and a network identifier (NID). For some networks, the base station identifiers (Base ID/SID/NID) may be transmitted via messages on an overhead channel. For example, in IS-95 and cdma2000 code division multiple access (CDMA) networks, the base station identifiers are transmitted via system parameter messages on a paging channel. For these networks the terminal is able to obtain the base station identifiers by processing the overhead channels. The terminal can report the base station identifiers can to the PDE. The PDE can use the identifiers to determine the approximate location of the terminal.
A terminal is typically on a traffic channel during active communication with the wireless communication network. For IS-95 and cdma2000 networks, there are no defined messages that may be transmitted on the traffic channel that can update all of the base station identifiers (Base ID/SID/NID). If the terminal is in active communication with the network for a length of time and has moved some distance to a new location, then the base station identifiers obtained by the terminal at the start of the data communication may be incorrect. If these out-of-date base station identifiers are reported to the PDE, then the PDE may provide incorrect aiding information to the terminal.
There is therefore a need in the art for techniques for updating base station identifiers for position determination purposes.